Space power applications have a variety of energy requirements, including steady power outputs and pulsed high energy outputs. Pulsed mode power operations require high energy power bursts for relatively short durations. The thermal management systems are required to dissipate the excess thermal energy produced during the pulsed operations. To accommodate the large amounts of excess thermal energy, large heat transfer and heat dissipating devices are ordinarily required.
Thermal energy storage devices have been proposed to reduce the size and mass of the thermal management system. In this manner, a portion of the reject heat from the primary power source or other system power components are placed in a thermal energy storage system during peak power production and power use. The stored heat may then be dissipated into space during a non-operational portion of the orbit which can be an order of magnitude longer than the pulse cycle. The thermal energy storage enables the heat rejection system to be sized for an orbital average duty rather than peak demand. The thermal management system can therefore be reduced in size and mass. In particular, a smaller radiator can be used since the heat rejection rate is reduced. The overall mass of the system can be reduced where the mass of the radiator is reduced more than the mass of the heat storage device.
Lithium hydride (LiH) has been proposed for use in thermal energy storage devices. Various aspects of LiH thermal energy storage devices are described in a publication entitled "Development of Encapsulated Lithium Hydride Thermal Energy Storage For Space Power Systems" by D. G. Morris, J. P. Foote and M. Olszewski, published December 1987 for the U.S. Department of Energy (U.S. Government Printing Office 1988-548-118/60135), and "Development of Encapsulated Lithium Hydride Thermal Energy Storage" by M. Olszewski, and M. Siman-Tou, published by IEEE (Proceedings of the 24th Intersociety Energy Conversion Engineering Conference - Vol. 6 - "Post Deadline papers and Index"). Both of these publications are incorporated herein by reference.
It was noted in the aforementioned publications that hydrogen gas (H.sub.2) formed by dissociation can be lost by passing through the encapsulating shell and, depending on the volume of H.sub.2 loss, overall efficiency will diminish.
In view of the above, a need exists for an improved thermal energy storage device in which free H.sub.2 created during dissociation is prevented from being lost.